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Astrodon - Photometric Sloan - 1.25" Gen 2 Parfocal UV Blocked Clear Filter


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Manufactured by: Astrodon


Astrodon Photometrics Generation 2 Sloan Digial Sky Survey Filters


The Sloan telescopic filters were first invented in 1996 to improve and enhance the slow wavelengths, specifically near the OI 557.7nm range. They consisted of colored glass filters and short-pass dielectric coatings that steepened the low bandpass length. Due to the magnificient results, the Hubble Space Telescope even uses this filter method to seek out extra celestial information in the cosmos. With its vast and expansive database, the massive and famous scope has been able to pinpoint and mark virtually every point in the sky (up to 23 magnitude) to create 3 dimensional map of the universe. Astrodon has now brought this technology to the amateur astronomer with their new photometric sloan generation 2 filters!


  • The Astrodon generation 2 filters feature band blocking from Tave<=0.1% to Tabs<=0.03%
  • 50%T points for the R and I filters
  • Astrodon has introduced Z_S filter that cuts out long wavelengths-826/920nm
  • Y filter 950/1058nm
  • New and advanced Z filter->820nm
  • Generation 2 photometric sloan filters reduce stray light reflection


Astrodon Photometric Sloan filters are only equipped with dielectric coatings that cause steep cutoffs at high wavelengths. and over 95% peaks. The two charts below explain the breakdown on how these new amazing filters work.


Product Series

The Sloan Digital Sky Survey (SDSS) filters were designed by Fukugita et al. (Ast. J., 411/4, April 1996, p. 1748-1756) to include five mostly non-overlapping filters covering 300 nm to the sensitivity limit of silicon CCD cameras near 1100 nm. They combined colored glass filters and short-pass dielectric coatings to steepen the low wavelength side of the bandpass. The [O I] skyline at 557.7 nm occurs between the g' and r' filters, and is thus reduced.


The SDSS photometric system is the most common filter set used today. The Hubble Space Telescope is equipped with an SDSS set that provides a large reference database for research. Much of photometry up to magnitude 23 will be done in this system with meter-class telescopes. The upcoming large collaborative survey projects (Large Synoptic Survey Telescope - LSST; Panoramic Survey Telescope and Rapid Response System - Pan-Starrs) will also use SDSS filters. The following is a summary of the 50% transmission points of a variety of SDSS filters from the Large Filter Consortium. The new Astrodon Photometrics Sloan set is included for comparison. The Astrodon Photometrics Sloan filters use only dielectric coatings to achieve steep cut-on and cut-offs and peak transmissions in excess of 95%.

  WIYN DES LSST Pan-Starrs Fukugita Astrodon
u'           320/385
g' 402/550 400/550 402/552 402/552 410/551 401/550
r' 560/710 560/710 552/691 552/691 556/695 555/695
i' 700/820 700/850 690/819 691/818 690/814 690/820
z' 830/980 830/1000 818/922 818/922 841/982 820/-


To minimize internal reflections that produce halos around brighter stars, the entire bandpass and blocking layers are deposited on one side of the substrate and a high-quality broadband anti-reflective coating is placed on the other side. These filters are parfocal with all Astrodon LRGB and narrowband filters. Specifications:

  • 50% transmission points provided above (+/- 3nm typical)
  • Peak transmission guaranteed > 95% (>90% for u')
  • <0.1%T out-of-band 300 - 1100 nm
  • Striae-free, single fused silica substrates
  • 1/4-wave propagated wavefront prior to coating
  • <0.5 arcminute substrate parallelism
  • 3.000 +/-0.025 mm substrate thickness
  • 1.25" mounted
  • 49.7 mm dia. unmounted
  • 49.7 x 49.7 mm square unmounted




Additional Information

Name Astrodon - Photometric Sloan - 1.25" Gen 2 Parfocal UV Blocked Clear Filter
Manufacturer Astrodon
Model C2-27R_gen2